Reference Signal Design for Channel Estimation in mMIMO
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Solution Overview
Problem
Current communication systems face challenges in accurately estimating channel impulse response (CIR) due to channel mismatch caused by UE mobility, especially in massive multiple-input multiple-output (mMIMO) systems, leading to interference and performance degradation in downlink data transmission.
Innovation Solution
A communication device configures sequences to achieve zero auto-correlation and zero cross-correlation zones, allowing for efficient channel estimation by phase rotating and mapping sequences onto subcarriers, ensuring minimal interference from other channel taps or signals, even when signals from different subsets are transmitted concurrently.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If UL SRS transmission is used for channel estimation in TDD mMIMO systems, then the need for CSI feedback is eliminated and implementation flexibility is improved, but channel mismatch error increases due to UE mobility between UL SRS and DL data transmission
Solution Approach 1:
The patent applies preliminary action by transmitting multiple UL SRS signals at different time instances before the DL data transmission. This allows the BS to perform channel estimation in advance and update the precoding matrix accordingly. The earliest arriving SRS signals are used for channel estimation, ensuring the precoder is as up-to-date as possible given the time gap constraints.
Solution Approach 2:
The patent employs periodic action by having the UE transmit UL SRS signals periodically at multiple time instances. This periodic transmission ensures that the BS receives updated channel information continuously, allowing it to track channel variations due to UE mobility and maintain accurate channel estimation for precoding.
2Loss of time
If the time gap between UL SRS transmission and DL data transmission is increased, then more time for processing is available, but channel mismatch error increases due to UE mobility
Solution Approach 1:
The patent uses preliminary action by performing channel estimation using the earliest arriving UL SRS signals before DL data transmission. This allows the BS to complete channel estimation and precoding matrix calculation as early as possible, maximizing the time available for processing while minimizing the time gap between channel estimation and DL transmission.
Solution Approach 2:
The patent applies dynamics by adaptively selecting which UL SRS signals to use for channel estimation based on their arrival times and the current channel conditions. The BS dynamically adjusts the precoding matrix based on the most recent channel estimates, optimizing the balance between processing time and channel estimation accuracy.
3Quantity of substance
If multiple non-orthogonal sequences are used for reference signals, then the number of supported UEs increases, but interference between sequences increases
Solution Approach 1:
The patent applies segmentation by dividing the set of non-orthogonal sequences into multiple subsets, where each subset contains sequences with controlled correlation properties. This segmentation allows the system to support more UEs by assigning sequences from different subsets to different UEs, while the intra-subset orthogonalization minimizes interference between sequences within the same subset.
Solution Approach 2:
The patent uses local quality by ensuring that sequences within each subset have specific local correlation properties (orthogonality or controlled cross-correlation), while allowing greater freedom between subsets. This local optimization of sequence properties reduces interference for UEs assigned sequences from the same subset, while the overall system can support more UEs through the use of multiple subsets.
Data Source
AI summary
The present disclosure relates to reference signal design methods and devices. In one example method, a first communication device obtains at least one sequence from a subset of sequences in a set of sequences and obtains at least one reference signal based on the obtained at least one sequence. The sequence is phase rotated during its generation, phase rotated in the frequency domain, or cyclically shifted in the time domain based on a constant value Δq. The first communication device transmits the reference signal to a second communication device.